Multiple-station transmission-circuits



W. H. HARDEN. MuLUPLEvsTATloN TRANSMISSION CIRCUITS.

APPLICATION FILED DEC. I3, I9I8.

PatentedSept. 27, 1921..

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UNITED STATES" xrizN'r OFFICE, f

WILLIAM n. HARDEN, OF BROOKLYN,` NEW YORK, Ass'IGNoR To AMERICAN TELE- PHONE ANn 'rELFGRAPH` OOMPAN To all Lo/tom t may @011.06m f Be it known that I, WILLIAM H. HARDEN, residing at Brooklyn, in the county of Kings and State .of New York, have invented certain Improvements in Multiple Station Transmission-Circuits, of which the following is a specification. p d d This invention relatesto systems for transmitting telephonie or telegraphic signals, and its object is to provide a system of this character giving improved service to a number of stations bridged across the line at various points. This is `accomplished by ya novel arrangement of circuits andapparatus for equalizing the transmission from the more distant stations 4to make it substantially vaseffective as from the tnearer stations. Y

e Theinvention isappliCable to a variety of situationsin which it is desirable that a station, say at one end of the line, have ready and effective communication with`all` of the other stations bridged upon the line yat varyving ldistances away,lasy for instance in train despatching systems or the like,and is espe- ,cially valuable for the order or call circuits `used by change areas. y y c c In the'latter case the circuit terminates in the telephone set of a B Operator WhOSe duty it is to complete, by the use of trunks, calls originating at various other stations or the operators inmulti-Oflice exexchanges and directed tosubscribers `associated with her exchange. To, do this she must be informed by the Apfoperator at the other exchange, ofthe number wanted and the exchangefrom which the call comes, and must in return advise the A Operator which trunk running .to her vexchange shall be used to completey the connection` This information is exchanged over ay call circuit. Such a circuit mayk extend from the B Operators set through al number of ex- I,

changes or stations, all of theA operators at each station having.VV access to the line There is therefore a possibilityfof a number of A operators coming onto the line at Once when the apparatus of each'being bridged across the circuit, cuts down the eHect-iveness of the connection between the others and the operator. Moreover inlarge citiesfthe stations may be widely separated and those more remote electrically 'from the -B..op

erator in question may easily be drowned out Specification of Letters Patent. Application filed December 1a, 191s.

Y, A. CORPORATION OF NEW YORK.

. VMULTIPLE-STATION TRANSMISSION-CIRCUITS.

Patented-sept, 27, 1921. serial No. 266,636'.

by the' nearer stations because of the greater volume of transmission from the latter.

The presenti invention remedies difficulties of the character indicated. It is hereillustrated as embodied in a cuit and will be more fully understood by vreference to the following description and the accompanying drawing which shows diagrammaticallyk a circuit emboding the inventlon.

Instead of the ordinary two wire circuit for connecting the variousstations I use a four` wire circuit indicated on the drawing generally at l. It is shown terminating'at one` end in 4a B operators station, B, wherel itmay be changed into a two Wire line 4by means ofL the usual three limbed transformer, 2; This vpermits the circuitto be connected to the standard two wire instrument, which changeably between this circuit and others Qo-f a Vdifferent character. The net-work?) is provided to balance the operators set (not shown) as is customary in using transformers of this kind. i

A1, A2, A3 and Ai4 indicate other exchanges or stations located at varying distances` from` x general they will not need to be inserted in ,any of the bridged circuits.

At each station orexchange the four wire circuit isV preferably converted intoa two y. Wire circuit 7 byja transformer 2 similar to the transformer 2 at station 3, and emltelephone call cir- Vployed for like` reasons.- Also, as at station c B, net-works 3 are providedtobalance the operators instruments.

Inasmuch as there are severalv operators at each of the VA stations any` number of whom may chance to come onto the call cir- .cuit simultaneously, the net-work` 3 at each station should bedesigned to give the best average balance under` the conditions likely;

Vvery bad condition of unbalance would to occur at that station. Experience indicates that asufhciently good balance may the depression by an operatorl of the callcircuit button which connects her instrument to kthe vtwo wire line 7, so that unless a l"station is actually using the line thetransformers or other apparatus of the station will not forma shunt for the talking cur- `rents-from other stations. IVithout providing a meansfor removing the bridges from the maincircuit when they are not in use a exist in the three limbed transformers 2 since normally no operators instrument is connected to the lines 7 to balance the net-work.

Auto-transformers 9 are placed in the line at each staten. Thel impedance ratio of these transformer coils "is high so that the loss to the transmission on the main circuit, due to the bridges is small. The loss, incident to the coil, in the station with which it is associated is made up by the amplifiers. It will be observedthat for all the stations yexcept/station A2 the auto-transformer is showny inl one side only of the four-wire bridge, the right-hand side.' The threelimbed transformer acts as a high impedance ratiorepeating coil and therefore the left- Y hand side of eachof the four-wire bridges shown connected to', the repeating'coil side of the three-limbed transformer does not need to be provided with auto-transformers.

Station A2 represents a special `case in this connection in that the three-limbed transformer is located at some distancefrom the inain four-wire circuit. The auto-'transformer 9 land theth'ree-limbed transformer Z have ratios such that reflection losses where these connect to the branch circuits The auto-transformers l0 have high Vimpedance ratios such that the bridgedlosses caused by these branch circuits vwill be small. The `presence of the Vamplifiers 5 and the length of thecircuits between these and station A2 prevent the use of high impedance ratio transformers at station A2 to accomplish this result.

An artificial line 11 is shown in the two wireleads of station A3. This device is use- 'ful forcutting down the number of ampli- `fiers necessary. In the'example given, for

instance, the amplifiers Gare designed to give the proper transmission from the more "distant station, A, and the artificial line 'is then added to the line atlstation A3 to make it the equivalent in transmission of the line running to station A4. The losses inci'- dent tothe `artficia'l line, as well as those due lto the auto-transformers, are unobjectionable because of the --peciiliar propertiesof the four wire circuit whereby they can bev eflicientlyfcompensated by the amplifiers.

It may be desirable in certain instances to have the circuit at station B` somewhat unbalanced. In the case illustrated in the drawing, for instance it will be noticed that, because of the one way repeaters in the branch leading to station A2, the operators at that station will be unable 'to hear the `operator at stations A3 and A* if they happen to be using the line and, similarly those at the latter stations cannot'hear those at station A2, unless the B -operators set and the net-work 3 are suiiiciently out of balance to repeat the talk back from the B station along theother side of the line from the one upon which Vit enters. The same unbalance will be necessary for this purpose, if the A stations use four wire instruments connected directly to the four-wire circuit, instead of the arrangement shown, as may be done, for instance, in a train` despatchingr4 system. It may be noted here that if it were desired also to use a fourwire instrument at the ystation B no opportunity for this imbalance would be present since the transformer 2 and net-work 3Jwould be omitted. In such a case the bridged stations would be isolated from eachother and to prevent interference a ,separate signal or lockout device of any approved; type could be employed. By using four-wire instruments kall limitations due to effects of imbalance are avoided, and lower equivalents between the B station andthe various A stations are, th'efore, possible, in general.

' Y here disclosed it is possible to render the transmission to all of the bridged stations equally effective, how-ever widely they may be separated, and lby reason of the peculiarities of the four wire line employedthe losses incident to the longer circuits and tot the apparatus used in connection with' the invention may be adequately compensated by the use of amplifiers, without the danger of singing which limitsthe degree of amplillic/ation practicable in the lordinary circuit.`

will be understood however that the invention contemplates the use of sections .of two wire circuit to complete theV connections wherever found desirable, and the means shown at each lstation for converting the four wire linepintoy a two wire line makes obvious the manner in which such an arran ement may be set up.

' 4 at I claim is:

1. In combination, Vva circuit comprising a section having separate lines vfor transmitting signals in opposite directions respectively, a plurality of stations some of which are bridged across said section of the circuit at various points 4and'meansv lassociated with the use of a circuit of the character the circuit for substantially equalizing the transmission from a selected one of said stations to each of the others.

2. In combination, a circuit comprising a section having separate lines for transmitting signals in opposite directions respectively, a number of stations bridged across the circuit at various points, one-way amplifiers so distributed in the opposite sides of the circuit that the effectiveness of the communication between a given station and each of the others is substantially the same.

3. The combination with a circuit having separate lines for transmitting signals in opposite directions'respectively, of a number of stations bridged across the circuit, means associated with the circuit for compensating the transmission losses from a given point thereon to the various stations to substantially equalize facility of communication with all stations, and means at each station forminimizing the transmission losses incident to bridging in on the circuit.

4. The combination with a circuit having separate lines for transmitting signals in opposite directions respectively, of a number of stations bridged across the circuit at various points, means associated with the circuit to compensate the unequal transmission losses from a given point on the circuit to the various stations, means whereby each bridged station may be disconnected from the circuit when not in use and means at each station for minimizing the circuit transmission losses due to the shunt formed by bridging in any station..

5. The combination of a telephone circuit having separate lines for transmitting sound in opposite directions respectively, a number of telephone stations bridged across the circuit, one-way amplifiers in the circuit located and distributed to compensate the unequal transmission from the various stations to a given point, auto-transformers interposed between the stations and the main circuit and switches whereby each bridged station may be disconnected from the circuit when not in use.

6. The combination with a main circuit having separate lines for transmitting signals in opposite directions, of a number of stations bridged across the circuit at various points, transforming apparatus at each station for converting the circuit into one communicating in .both directions over the same conductors and means associated with said main circuit for substantially equalizing the transmission from a given one of said stations to each of the others.

7 The combination with a main `circuit having separate lines for transmitting signals in opposite directions, of a number of vstations bridged across the circuit at various points, transforming lapparatus at each station for locally changing the circuit into one communicating in both directions over the same conductors, the transforming apparatus of one station being unbalanced to cause signals received over one side of the main circuit to be repeated back over the other side.

8. The combination with a four-wire transmission circuit having a number of bridged stations, of amplifiers distributed in the circuit and located adjacent certain of the stations, means for converting the four-wire circuit in each of the bridges into a two-wire circuit and artificial lines in the two-wire circuits of the stations adjacent the ampliiers for rendering them the equivalent in transmission of the stations more remote from the amplifiers.

In testimony whereof, I have signed my name to this specification this 11th day of December-1918.

WILLIAM H. HARDEN. 

